The present disclosure relates to gas turbine engines, and in particular, to a fan case for a gas turbine engine.
The fan of a gas turbine engine includes an array of fan blades which project radially from a hub within a fan case. Although exceedingly unlikely, it is possible for a fan blade or a fragment thereof to separate from the hub and strike the fan case.
The demands of blade containment are balanced by the demands for low weight and high strength. For relatively small diameter engines, adequate containment capability is typically achieved with a hardwall design in which a metallic case thick enough to resist penetration by a blade fragment is utilized.
For relatively large diameter engines, a metallic case thick enough to resist penetration is prohibitively heavy. Therefore, a softwall design is utilized in which a light weight, high strength ballistic fabric such as KEVLAR (a registered trademark of E.I. DuPont de Nemours & Company) is wrapped in multiple layers around a relatively thin, penetration susceptible metallic case. In operation, a separated blade fragment penetrates the case and strikes the fabric. The metal case is punctured locally but retains its shape and structural integrity after impact. The punctured metal case continues to support the fabric and maintains the clearance between the blade tips and fan case.